It is the purpose of this project to delineate at the cellular and molecular level the mechanism of action of microbial components in immunopotentiation. Four major approaches have been undertaken: 1) the determination of in vivo and in vitro activation of macrophages by fractions isolated from mycobacterial and rickettsiae, 2) measurement of chemotactic activity in vivo and in vitro of defined esters of trehalose isolated from a variety of mycobacteria, 3) chemical synthesis of analogs of these trehalose esters and 4) characterization of the biological activity of these analogs.